Cable conductor system



NNN-N ATTORNEY Patented June 27, 1933` narran sra'rss PATENT oFFicEHAR-RY lYQUST, QF MIL'LBUR-N, NEW JERSEY, ASSIGNOR T0 AMERICAN TELEPHONEAND TELEGFAPH COIJIPANY, .A CORPORTION OF NEVJ YORK CABLE CONDUCTORSYSTEM Application filed December 17, 1931. Serial No. 581,741.

It is among the objects of my invention to provide a new and improvedsystem for connecting successive lengths of conductor pairs or quads ina cable so as to improve transmission and facilitate adjustments in suchpairs or quads. Another object in such a system to remedy far-endcross-talk between such sets of conductors. Another bject of myinvention is to provide for oo nnecting successivelengths of conductorpairs or quads progressively with respect to capacity or other reactanceproperty so as to equalise all such conductor sets and facilitate thereduction of far-end cross-talk. Still another object of my inventionhas relation to further equalization or compensation for farendcross-talk by introducing lumped impedance devices in connection withsuch conductor sets. Allthese objects, and other objects and advantagesof my invention will become apparent in connection with the followingdisclosure of a limited number of specific examples of practiceaccording to the invention, which l have chosen for disclosure in thefollowing specification. It will be understood that this disclosurerelates principally to these particular examples of the invention, andthat the scope of the invention will be indicated in the appendedclaims.

Referring to the drawing, Figure 1 is a diagram showing a system ofconnections for Vsuccessi e lengths of conductor pairs in a cableaccording tol my invention; Fig. 2 is I a diagram showing supplementarymeans for equalizing the impedance ofconductor pairs repeaters; Fig. 3is a diagram illustrating the nature of asymmetrical far-endcrosstall;-Fig. s is a diagram showing a device for correct-iigsymmetrical far-end crosstalli; Fig. 5 is a diagram showing a device forcor 1ecting asymmetrical far-end crosstallr; Fig. 6 is a diagram showinga device to reduce reactionr cross-talk; and Fig. 7 is diagram to showthe nature of dilerent kinds of cross-talk.

lnlaying a multi-conductor cable, successive reel lengths are placed endto'end and the pairs in one reel length are' spliced to correspondingpairsv in the nemJ reel length to provide continuous conductor pairsthrough a number of such reel lengths. For example, a cable may have 68pairs and between two successive repeater stations, it may consist ofy300 reel lengths spliced together at`299 junctions.

` A. pair in one reel length is likely to vary somewhat in capacity perunit length as compared with a pair in another reel length. If suchpairs are splicedv together, it means that successive line sections areof different impedance and there are, accordingly, reflections of energyat the various junctions. The. most obvious method of connectingsuccessive'sections is to connect them together at random. However, thisresults in large reflections in some cases. They system here to bedescribed maybe explained by means of the specific example, namely, 68pairs in 300 reel lengths, as mentioned above.

Each yof the 68 pairs in one reel length is tested for capacity andthese pairs in this reel length are designated in theorder of theircapacities. In Fig. 1, the cable is represented` diagrammatically asextending lengthwise horizontally across the figure. Each dot representsa pair in a reel length; thus a column of dots represents a completereel length. These pairs in a single reel length, represented by acolumn of dots, are to be thought'of asarranged in the'order ofdescending capacity from top to bottom. Thus in reel length numbered 5,the pair of highest capacity is represented by the dot at the top `ofthe column, the pair next highest in capacity by the next dot in thecolumn, and so on, the pair of lowest capacity being represented by thelowermost dot in the column.

Beginning at the left-hand end, the pairs in the first reel length areconnected to those inthe second reel length, as indicated by the linksjoining the dots at the left of Fig. 1. Thus pair l in the'first reelllength is connected to pair 3 in the secondvrcellength, which in yturnis connected to pair 5 in the third reel length, and soon. Theseconnections beginning at the left and extending as far as reel' lengthl0 are fully indicated in the left part of Fig. l and will require nofurther verbal description. 1

If the connections were continued through the whole length of the cable,according to the plan that has just been described, then pair 1 in thefirst reel length would eventually be connected with pair 68 of lowestcapacity in thethirty-fifth reel length,y and in thirty-three more reellengths, that is, in lel length No, 68, the continuous conductor vpairfrom the beginning would have beenshifted from a pair of highestcapacity, namely, pair l in reel length 1 to a pair of lowest capacity,namely, pair 68 in reel length k35, and then back to a pair of next tothe lowest capacity, namely, pair 2 in reel length 68. Such a cycle willbe called a wave. Continuing in this way, four times 68, or 272 reellengths, would-make four complete waves or cycles, leaving twenty-eightmore reel lengths to be connected'. It is desirable .to come out with apair at the distant end'oftlle' Cble at the saine level at which we wentin and, therefore,

twenty-seven straight 'connectionsl are dis,V

tributed uniformly along the length ofthe cable, as shown for one suchconnection in Fig'l between the reel lengthsnumbered 10 and 11 le havejust ymentioned that four complete waves or cycles willvcarry us fromreel length 1 to reel length 272. But 1nterspersing these twenty-sevenstraight connections will carry us to reel length 299, and continuingaccording to the wave plan into reel length 300, will bring.v us topositions at the right corresponding exactly with those for thesame-conductor pairs at the left; that is,

i thepair that begins. at the left at highest capacityl in reel lengthlfwill come out at the right in thepair of highest capacity 1 1n reellength 300, and'similarly for other pairs.

As already mentioned, there are twenty? A seven straight connections tobe distributed in 300 reel lengths.: f j p There will be V28intervalsbetween the ends and the straight connections and hence the number ofreel lengths between consecutive straight connections ywillbe an integern ear BOO/28 which is 10 and 20/28. Multiplymg this by 1, 2, 3j, etc.for successive intervalsthe numbers 10 and-2'0/28, 21 and 12 /28, 32 and4/28, et'c. are obtained. The straight connections will accordingly belocated between the 10th and 11th reel lengths, between the 21st and22nd,'between the 32nd and 33rd, and

so on. f

Of coursethe impedance of a pair isV dependent on inductances as well ason capacity. But the capacity and inductance are correlated ratherdefinitely. If we think of the two conductors' as being moved furtherapart to decrease the capacity between of that'circiuit at the Sametimeand in about the same ratio. Thiswill be the justificationv for .fixingour attention on the capacity in the followingy Vdiscussion and sayinglittle directly about the inductance.

It will be apparent that the circuit of each pair in the system built upaccording to the foregoing plan will be relatively free fromreflections, for the capacity of the pair in one reel length will bevery little different from the capacity of the pair in the consecutivereel length so there will be very little impedance difference atjunction points to occasion reflections. Moreover, the sixttyeightcircuits will be substantially equal in total attenuation because eachcircuit-pair goes four times through the cycle from highest to lowestimpedance and thus the circuit pairs are substantially alike. However,there will inevitably be some difference between thepairs in terminalimpedance, that is, in the impedance presented by a pair at the terminaloffice. In order to get the benefit of the kind of splicing that hasbeen described, the ofiice impedance connected to the different pairsshould be made adjustable and should fit the impedance of the pair inthe nearest `reel length as nearly as practicable. A convenient way ofdoing this is to build the repeater so that its output impedance fitssubstantially the lowest impedance that will be encountered and itsinput impedance fits substantially the highest impedance that will beencountered. Then the repeaters can be built out as indicated in Fig. 2by series resistances on `the output side and shunt resistances on theinput side, these resistances being adjusted to fit the line. In thisway,

repeater, and vice versa for kcircuits which are ofv high impedance atthe ends. As a result, the total building out connected to any circuitwill tend to be approximately constant and the total attenuation of the.line, including the building out resistances;

at b othends, will tend to be constant, as com- 'paring one pair withanother among the sixty-eight p airs.

In order to get the fullest advantage of this type of splicing, itshould be combined with allocation of reels. by measuring the averagecapacity of the pairs in available reels and then arranging the reels sothat no two reels having widely dierent average capacity per unit lengthare adjacent to each other. lThe preferred arrangement is to arrange thereels in ascending or descending order of average capacity per unitlength. However, such a complete allocation would be ratherinconvenient, and would be unnecessary unless extreme avoidance ofirregularity were desired.

It will readily be seen that the foregoing system for 300 reel lengthsand sixty-eight pairs might be modified by introducing a greater numberof straight splices and having a less number of complete waves or cyclesThis can be done v other v pair.

from end to end of the system. However, there should be an integralnumber of these waves orl cycles in any case and it will be better not`to have the number too small, as for example, merely one complete waveor cycle, for in the case of only one complete wave or cycle thecross-talk between two pairs may be asymmetrical. This is illustrated inFig. 3 where two pairs l and 2 are represented'. extending between thepoints A and B. The networks in these pairs represent excessiveattenuation at the points where they are placed. lt will readily be seenthat far-end cross-talk from A-l to B-2 suers attenuation through boththe networks, whereas far-end cross-talk from -A-2 to B-l is notattenuated in either network. The result will be greater'far-endcross-talk from A-2 to B-l than from A-l to B-2- But in the correctionof cross-talk, it is far more convenient to have it symmetrical. Suchcorrection may be effected, for example, as shown in Fig. 4 by aninductive linkage between a properly chosen conductor of one pair and aproperly chosen conductor of the Such correction is obviouslysymmetrical and, therefore, if the far-end cross-talk is not symmetricalit cannot be accurately vcorrected in this way. Thus an advantage of themultiple Vwave system, indicated in Fig. l, is that it tends to reduceasymmetric far-end cross-talk and makes correction practicable by suchmeans as shown in Fig. 4.

If the number of reel lengths is small compared to the number of pairs,the shifts at `each junction may be made greater than in Fig. l, so asto get enough complete waves from end to end. For eXample, mstead ofconnecting from l to 3 at the upper left corner of Fig. l, we mightconnect from l to 5 and so on. Also, should it be desired to reduce thenumber of waves from end to end, more straight connections may beintroduced, either one at a place, or two or more consecutively atplace, these places being distributed uniformly. y

` It is practicable to introduce an asymmetric corrector for asymmetricfar-end cross-talk if the need becomes inevitable. ln Fig. 5 we see thesame series transformer at vthe left as in Fig. 4 and, in addition,another transformer with one winding in series in one conductor of pairvl and the other winding bridged across the conductors of pair'2 with a4resistance in series. If the two transformers are poled so as tobeseries aiding in transmission from A-l to B-2, and as indicated by thesolid line arrows, then they will be opposing in transmission from A-2to B-l, as indicated by the dotted line arrows. Accordingly, the far-endcross-talk components due to the corrector shown in Fig. will be greaterfrom A-l to B-2 than from `Af2 to'B-l-and will therefore correct normalfar-end cross-talk which is asymsents ordinary far-end cross-talk. Thereisl anothervvariety of far-end cross-talk which arises from near-.endcrosstalk with one reflection. This is shown by thearrows c and d,according to whether the reflection occurs in the first pair or thesecond pair. Such reflection far-end cross-talk appears as ordinaryfar-end cross-talkexcept that'it will be somewhat displaced in phase.Reaction cross-talk is as represented by the arrows e and Here a thirdpair 3 is involved, and in the first stage as shown by arrow e, there isordinary near-end cross-talk from pair l tofpair 3. Then again there isanother Stage of near-.end cross-talkfrom ,pair 3 to pair 2, giving aresultant far-end cross-talk from pair l to pair 2. Similarly, as shownby arrow fr, reaction far-end cross-talk may arise as theresultant oftwo stages vof farend cross-talk. i

The ordinary far-end cross-talk as represented in` arrow b can. beeliminated to a large extent by means of balance, as suggested in asimple manner in Fig.'4. The reflection cross-talk such as indicated bythe arrows c and Z in Fig. 7 can be minimized by avoiding impedanceirregularities in the line which would give rise to reflections. This.is accomplished in the foregoing described system of Fig. 1. It is to benoticed that reaction cross-talk such as represented by arrowse and finvolves a third pair in addition to the two pairs between which thecross-talk occurs. This intermediate pair, instead of being physicallydistinct as in Fig.7, `may be a useless phantom on pairs 1 and 2, or auseless phantom between one of these and a third pair such as l and v3;or the intermediate circuit may be a circuit established by adegree ofgrounding of one or more pairs. lllhen the intermediate circuitrepresented by 3 in Fig. 7 is a physical pair, the reaction cross-talk,'represented by y e, will be relatively small Afor the reason thatnear-end cross-talk is known by experience to be small enough so thattwo such stages of near-end cross-talk in tandem would not be great.Therefore it is inferred that the chief intermediaries in the case ofreac- Ytion cross-talk, represented symbolically by conductorsthereof,whereasA the normal useful voicecurrents flow in opposite phase in thetwo conductors of a pair. Accordingly, a transformer system such asrepresented in Fig/6,v is interposed in each pair. For thevnormaltransverse currents of the pairs it will be seen that the two windingsin the respective conductors of the pair buck each other, `so that theyhave practically Ano reactive effect.` :But for currents flowing in thesame direction in `the twoconductors, these windings are series aidingon the magnetic circuit and, therefore, an inductivereactance is setup.The third winding on the core Vhas a `resistance in series therewith sothat the fiuxset up' in the core by the phantom currents leads to adissipation of energy'in the resistance. 'In this yway 'the normaltransverse. voice currents are i not damped by the device, ybut theabnormal or parasitic .phantom currents have their energy dissipated inthe resistances. These'devices, such as `shown in Fig. 6'will beinserted in 'allthepy airs in the cable 'at suitable intervals which maylbe at every splice, or at iintervals of a few reel lengths. Theneter'ect ofthe application of these devices 'in all the pairs is toincrease the attenuation in all circuits other than pairs, withoutimpairment ofthe normal current flow in the pairs. Inasmuch as theintermediate or third medium in reaction cross-talk is generally somesuch othercircuit, the devices will serve ygreatly to reduce thereaction cross-talk.v Y

The two interposed windings of the deviceshown in Fig. 6 should be asnearly perfectly coupled aspossible so that the inductance Vtotransverse currents in the ypair will be negligible. Moreover, thesewindtingsshould have as low-a capacitytas .possible. 'the capacity andthe leakage inductance negligible, the coil should be designed s o thatits characteristic impedance will beequal hto that of the pair. t n

The foregoing disclosurehas had relation principally to smooth lines.Such lines may be worked` with carrier currents at high fre- `quencies,for which the capacityA eliects be- :tween the conductors 'of a pairbecome considerable, and the proper joining up of successivey reellengths according to my invention `becomes of considerable.importance.Tov a degree, the principlesof my invention may be utilized for loadedlines with' cable pair sections extending between the loading coils. Inthis case the current frequencies will `not be as high as for smoothcarrier current circuitsandthe capacity reactances will not be 'as high,andA therefore, :it ybecomes unimportant to systematize the .splic-y ingbetween'reel lengths. But thel same system of splicing. between reellengths that is disclosed in connection with Figl for smooth lines 'may`ad'vantageo'usly "be employed for loading*sectionsofloaded lines.'V

If it is notpossible vto make both The .principal aim of wave splicingin the' case of high frequency carrier cables is to reduce reflectioncross-talk.V In the case of loadedcircuitsthe aim is to have the linepresent a' smooth impedancelto the repeater oiice, which makes itsuitable for two way operation. Here we deal with two wire circuits withtransmission both ways, whereas in the case of the smooth lines`heretofore considered we dealt with one-way transmission infour-wire'circuits.

The loaded lines here considered will enerally be `phantomed so that wemust eal with quads, each quad comprising two side circuits.` Aprocedure in accordance` with my invention .willrbe to complete all theintermediate splices but without the loading coils connected at eitherend, lthen measure the capacity between the two conductors of each side.circuit pair in a given group in each loading section, then add thecapacities of the two side circuits in each quad. Call thequad for whichsuch added capacities give the highest result, No. l, the next No. 2,then No. 3, and so on. Measure the circuits and number the quads in thesame way in all the loading sections. For convenience let us assume a.particular loading coil station and let the numbers stand as thusVobtained on the east but let them be primed, that is, l', 2, 3', etc.,on vthe west. Assuming that the cable has fourteen quads', let thembeconnected at this loading coil station according to Vthe same generalplan as in Fig. l, but without straight splices, that is, in accordancewith the followingtable.

vVpVithin each quad, pole the'pairs so 4that the pair .with the highestcapacity in that quad goes to the pair of the highest capacity in thequad of the associated section according 'to the above table. Y

It has beenstated above thatffor 'loaded lines with their lowerfrequencyyas'compared with smooth carrier current lines, there is y.no advantagein wave splicingfor connecting the reel lengths between loading coilstations. It may properly betconsideredthat this Vis because the phaseshift in all the reel lengths making up one such section iscomparatively small, and this is due to the .fact

pensatory manner so that the total capacity pern loading section is asnearly the same as practicable,y for all the different circuits.Suppose, for simplicity, that a cable is made up of pairs only, that is,no quads. Suppose, further, that one'loading section comprises eightreellengths. Then a simple procedure is to connect the rst reel lengthto the second, the third to the fourth, the lifth to the sixth, and theseventh to the eighth, so that the highest capacity pair in the firstreel length is connected to the lowest capacity pair in the second, thenext highest in the first is connected to the next lowest in the second,and so on. After this, the junctions of the second to the third and thesixth to the seventh may be made according to the same procedure, havingregard to the capacities of the double length sections that have beenestablished to this point. Finally, the fourth and fifth lengths may beconnected in the same Way, having regard to thecapacities of thequadruple length sections that have been built up to this point. Theadvantages of this kind of connection may be reached to a degree butsufficiently, by taking part of these steps but adopting random splicingto some extent. It is also desirable to make use of allocation of reelsin such a manner as to make theaverage capacity the same in all loadingsections.

Usually the deviations in the loading coils do not cause as greatirregularities as the deviations in the line capacities. When the latterhave been taken care of, as disclosed heretofore, it--may be that theloading coils will contribute enough irregularity to make it desirableto systematize their connections. First assume that the loading coilsare substantially alike in respect to n' capacity, and grade themaccording to Iinductance. In this case increased uniformity can beobtained according toeither of two plans. The first plan is to connectthe highest inductance coil between the highest capacity pairs, thesecond highest inductance coil between the next highest capacity pairs,and so on. The second plan is to connect the highest inductance coilbetween'the lowest capacity pairs,ythe next highest coil between thenext lowest pairs, and so on. The first plan is thought preferable whenthe cut-off ofthe lo-ading is high in` comparison with the highest fre-'q'uency used. `WhenA the cut-oill frequency Vco is only slightlygreater than the highest frequ'encyv used, the second plan is thoughtpref'- erable.

But there may be variations in the coil ca- .pacity of sufficientimportance to be considered. In this case the coils are arranged n asbefore from highest to lowest but instead of having regard only to pureinductance they are arranged in Vdescending order of the quantityL-RZVC, where L Iis the coil inductance, R is the characteristic`impedance of the line, and C is the coil capacity. The

propriety of this formula will be recognized whenit is remembered` thatcapacity annuls a certain fraction ofthe ,inductance, this fractionbeing approximately R2/C. Hitherto it has been assumed that the cable ismade up of pairs exclusively. In a more usual case, however, the; cableis made up of quads, and the coils are made up in phantom units. inorder to have a useful phantom circuit it is necessary to take care thatthe two pairs in a quad are not separated in any of the splicesand,lilrewise, that the two pairs in a quad are connected to the loadingcoils which form a unit. Therefore, the procedure out-lined above willnot be applicable in suzh a-case of quads, for if it were followed itwould separate the pairs. The procedure to be followed in the case ofquads ymust be a compromise as, for example, in

accordance with the following plan.

In the first place it will be assumed that it is ly, the fourth groupcontains those ten quads in which the difference between'the sidecapacities is the greatest. v

Next, each group of ten quads is .arranged according to the order of thesum of the side circuit, capacities so that the quad which has thehighest sum for the side circuit capacities within any group of ten isassigned the number l, etc. In splicing within any loading section,quads incorrespo-nding groups arelspliced together and within a givengroup a quad having the highest sum is spliced to the one having thelowest sum, etc., and within the quad high pair is spliced to a lowpair. At the loading points the practice of wave splicing Vis applied tothe quads in accordance with the sum of the capacities of their pairs,as heretofore explained.

In respect to the manner of splicing the pairs within a given quad, thefollowing procedure is suggested in cases where the correlation betweenthe capacities ofthe two pairs of a quad is small. At each third loadingpoint, say at points l, 4, 7 etc., high is connected to high within thethree groups of ten connected to low at these points. At the loadingpoints numbered 2, 5, 8, etc., high is connected to high throughout thequads in group 4 are connected to the quads in group 3 and the quads ingroup 2 are connected to manner the construction will be that of asmooth wave. Y

If it should be deemed desirable to iinprove the smoothness of thephantoms as well as of the sides, this may be done by confining the wavesplicing to either the sides or the phantonis and then to obtain thesmoothness in the vphantoms or the sides, respectively, by means ofsplicing within the loading sections.

I claim:

1. The method of'connecting a plurality of conductor sets in successivesections of a cable, which consists in connecting them progressivelyaccording to a reactance property of such sets from higher to slightlylower and so on and then back from lower to slightly higher and so on inan integra-l Vnumber of completewaves.

2. The method of conductor sets in consecutive cable sections, whichconsists in numbering the sets in each section in order of a reactanceproperty, then connecting Vthem progressively 1-3-5 etc., 2-1-3 etc.,3-5-7 etc.,4-21 etc., and so on through all the numbered sets in thefirst, second and third sections, and so on through all the sections.

3. The method of claim 2, with the quali- `fication that straightconnections are interspersed uniformly, the number o straightconnections being such as to make an integral number o 'complete wavesof progressive connections. f

f4. A multi-conductor cable in sections end to end, a plurality of setsof conductors in each section being graded in respect to ak reactanceproperty and the sets of conductors of these sections being connectedprogressively at the section junctions according to the grading.

5. A multi-conductor cable in sections end kto end, a plurality ofsetsfof conductors-in each section being, graded in respectto areactance property and the sets of conductors of these sections beingconnected progressively at the section junctions according to thegrading, kthe progression being carried over at least one complete Wavealong the length of the cable.f

6. A multi-conductor cable in sections end to end,a plurality ofl setsof conductors in each section being graded in respect to a reactancepropertyand the sets of conductors of these sections being connectedprogressively at the section junctions according tothe grading, theprogression being carried' overyan integral number of complete wavesalong the length of the cable.

A'i'. A cable comprising a plurality of sections `end to endwithaplurality of conductor sets in each section, the sets in each sectionconnecting a plurality of Y being graded in respect ltoareactancegproperty andthe sets beingconnected'consecutively fijomsection to section in progressive order based on such grading,the/progression ,extending to an eXtreme of the graded prop- Ierty, thenreversing, and so on through 'at least one complete cycle.

8. A cable as defined in cl'aim 7 with alternative straight connectionsat enoughof the junctions to establish an integral number of completecycles'from end'to end.

9. In a multi-conductor cable, sections connected consecutively, a pairofa certain capacity in one'section being connected to ay pair l Vofslightly difiere-nt capacity in the next section and so on progressivelyfrom section to section until an extreme of capacity has been reachedand then in opposite progression until the opposite eXtreme has beenreached, the l connections being carried thus through' an integralnumber of complete waves or cycles from one end of the lcable to theother.

10. A cable according to claimy 9 with straight connections intersperseduniformly so that the progressive connection will come' out in anintegral number of complete waves. 11. A multi-conductor cable insections end to end, sets of conductors in each section being graded inrespect to a reactance property, r

and the sets of conductors of thesesections being connected at thesection junctions progressively according to the grading to sets ofconductors of small reactance difference, so as to afford only slightimpedance irregularities at the junctions and so as to givesubstantially the same attenuation inthe connected sets of conductors. n

Y 12. Two cable lengths, each according to claim 11, and betweenV them arepeater built to fit a low impedance on its output side, and ay Vhighimpedance on its input side,and an adjusted series impedance interposedon its output side, and an adjusted shunt resistance across its inputside.

13. A cabley according to claim 11, and cor-` rectors for residual jasymmetric far-end cross-talk interposed between the conductor setsthereof.

14. A cable according to claim 11, andapparatus units interposed in theconductor 5 sets, these units offering substantially no impedance totransverse' currents on'the sets but beingenergy dissipators forlongitudinal currents on the sets.

15. Means for equalizing asymmetric far` end cross-talk between twoconductor pairs, consisting of two transformers one having its two coilsrespectively in series in conductors of the respective pairs and theother transformer having one coil in series in one conductor of one pairand the other coil across the other pair, and a resistance in serieswithY the last mentionedcoil.

16. Means for equalizingasymmetric far-- end, cross-talk between twoconductor pairs;

Tino

comprising a reactance connection and an energy dissipator, said energydissipator functioning to dissipate energy for far-end crosstaik one Waybut not for far-end cross-talk asymmetric thereto. A f

17. Means for equalizing asymmetric farend cross-talk between twoconductor pairs consisting of two transformers, their coils beingconnected with conductors of the pairs and pole-d to be aiding forfar-end cross-talk one way and opposing for asymmetric farnd cross-allthe same way.v

18. A transformer system to be interposed in a multi-conductor cabietoremedy asymmetric far-end cross-talk, having at least three coils and aresistance in series with one coil. Y n

19.` Means to remedy reaction far-end cross-talk between conductor pairsconsisting of a transformer in each pair with one winding in one side ofthe pair, another winding in the other side and a third winding incircuit with a resistance, the windings in the sides bucking each otherfor transverse currents in the pair.

20. Means to remedy reaction far-end cross-talk between conductor pairsconsisting of a transformer in each pair wound to be non-reactive totransverse currents and energy dissipative to longitudinal currents.

In testimony whereof, I have signed my vname to this specification this15th day oitl December, 1931.

HARRY NYQUIST.

